The present invention relates to a circular knitting machine for knitting hosiery or the like, with a device for producing tubular items closed at an axial end and to a method for producing tubular items.
It is known that hosiery items, according to the conventional method of production with circular hosiery knitting machines, are unloaded from the machine that produces them with their toe open and must then be subjected to stitching or looping on appropriate machines in order to obtain the finished product.
In view of the fact that the toe stitching or looping operation significantly affects the overall production costs of hosiery items, methods and machines which allow to obtain closed-toe hosiery items directly on the machine that produces them have been studied and improved in recent years.
One of these methods is disclosed in Italian Patent no. 1,286,604 and substantially consists in forming the hosiery item on a single-cylinder circular machine by starting from the toe and formation initially a pocket by using the needles that belong substantially to one half of the needle cylinder. The initial border of the pocket, at the end of its formation, remains free inside the needle cylinder, while the final border of the pocket is retained on the needles of the half of the needle cylinder that formed it. The initial free border of the pocket is subjected to suction in a region located inside the needle cylinder. Substantially, a region of concentrated air suction is provided inside the needle cylinder and gradually affects the initial free border of the pocket as a consequence of the rotation of the needle cylinder about its own axis with respect to said concentrated air suction region. In this manner, the initial free border of the pocket is captured and gradually engaged by appropriately provided elements being constituted by particular lowering sinkers which have a point at the upper end of their nose. By the action of these lowering sinkers, the initial border of the pocket is gradually transferred above the needles of the half of the needle cylinder that did not form the pocket, so that through subsequent lifting of the needles said initial border of the pocket is crossed by the needles that did not take part in the formation of the pocket. At the end of this operation of transferring the initial border of the pocket onto the needles of the half of the needle cylinder that lies opposite the half used to form the pocket, the entire border that delimits the pocket is engaged with the needles of the needle cylinder, which are actuated so as to continue formation of the item in the conventional manner, thereby forming a hosiery item which is closed at its toe.
The concentrated air suction region, in known types of machines that perform this method, is generally constituted by a suction port, the intake whereof is located proximate to the upper end of the needle cylinder and has a profile which, according to the rotation of the needle cylinder about its own axis with respect to the suction port, gradually approaches the cylindrical wall of the needle cylinder, so that the initial border of the pocket, by engaging said profile, is gradually moved toward the needles designed to receive said initial border of the pocket, in order to allow the lowering sinkers, provided with said point, to engage said initial border in order to transfer it above said needles.
For the successful transfer of the initial border of the pocket to the needles designed to receive it, such initial border must remain constantly engaged with the profile of the suction port. If the initial border, as a consequence of the knitting process and of the yarns used for its production, is not sufficiently resilient, said initial border can disengage from the profile of the suction port, and therefore the initial border of the pocket, instead of moving gradually toward the needles that must engage it, escapes toward the axis of the needle cylinder, making it impossible for the lowering sinkers to engage it and thus making it impossible to transfer one or more parts of the initial border onto the needles that are designed to receive it.